DESCRIPTION: The overall goal of this grant application is to determine the mechanisms whereby differentiation and terminal growth inhibition are controlled and to elucidate how neoplastic transformation arises in epithelial cells. When primary mouse keratinocytes are placed into suspension culture they undergo differentiation and terminally growth arrest which is accompanied by a rapid increase in p27kip protein and cyclin/cdk inhibitory activity. In addition, the cyclin A and cyclin D1 proteins undergo rapid degradation which is reflected in the loss of their associated kinase activities. Specific aims are designed to characterize the p27kipkip associated Rb kinase that Dr. Pledger hypothesizes is required for differentiation and to determine the mechanism that regulates the degradation of cyclin A and D1. The p27kipkip Rb kinase activity is brought about by an association of p27kipkip1 with cyclin D3, and the mechanism by which this association is regulated will be elucidated and its role in differentiation will be determined. Dr. Pledger proposes that loss of cyclin/cdk activity brings about growth arrest. Therefore, experiments are proposed to determine the factors that result in a loss of cyclin protein and activity in primary mouse keratinocytes. The correlation of cyclin degradation to growth arrest has been made in that primary mouse keratinocytes arrest immediately in suspension while MK cells, an immortalized mouse cell line, completes S phase and SLC-1, a tumorigenic cell line, continues to grow. Primary cells have a functional cyclin degradation system whereas the tumor cell line does not. Thus, the role of cyclin degradation and cyclin/cdk activity in growth control will be evaluated. Lastly, oncogenes will be used to determine which oncogenes and their associate pathway can alter cell cycle control and which ones modify normal cyclin/cdk regulation.